xfsprogs: fix crc32 build on big endian

xfsprogs: fix crc32 build on big endian

While kernelspace can test #ifdef __LITTLE_ENDIAN, this
doesn't work in userspace.  __LITTLE_ENDIAN is defined -
as is __BIG_ENDIAN.

So we build on all boxes as __LITTLE_ENDIAN, and the
self-test (thankfully!) fails on big endian boxes.

Fix this by testing __BYTE_ORDER values.

And add an else which should never be hit, but just in case...

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Rich Johnston <rjohnston@sgi.com>